General Chemistry IIA: Practice Exam 1

Colligative Properties and Solution Chemistry

Freezing Point Depression and Boiling Point Elevation

Colligative properties depend on the number of solute particles in a solution, not their identity. Two important colligative properties are freezing point depression and boiling point elevation.

• Freezing Point Depression: The freezing point of a solvent decreases when a non-volatile solute is added.

• Boiling Point Elevation: The boiling point of a solvent increases when a non-volatile solute is added.

• Equations:

$\Delta T_f = -K_f m$ $\Delta T_b = K_b m$

• m = molality of the solution (mol solute/kg solvent)

• K_f = freezing point depression constant

• K_b = boiling point elevation constant

Example: Calculating the freezing and boiling points of a solution containing ethylene glycol in water.

Vapor Pressure and Raoult's Law

Raoult's Law describes the vapor pressure of an ideal solution:

$P_{solution} = X_{solvent} P^0_{solvent}$

• Vapor Pressure Lowering: Addition of a non-volatile solute lowers the vapor pressure of the solvent.

• Clausius-Clapeyron Equation: Used to relate vapor pressure and temperature:

$\ln\left(\frac{P_2}{P_1}\right) = -\frac{\Delta H_{vap}}{R}\left(\frac{1}{T_2} - \frac{1}{T_1}\right)$

• ΔHvap = enthalpy of vaporization

• R = gas constant (8.314 J/mol·K)

Intermolecular Forces

Types of Intermolecular Forces

• London Dispersion Forces: Present in all molecules, especially significant in nonpolar molecules.

• Dipole-Dipole Interactions: Occur between polar molecules.

• Hydrogen Bonding: Special type of dipole-dipole interaction; occurs when H is bonded to N, O, or F.

Example Table:

Component	Intermolecular Forces
CH3OH	Hydrogen bonding, dipole-dipole, London dispersion
CH3Cl	Dipole-dipole, London dispersion
CH4	London dispersion
HCl	Dipole-dipole, London dispersion
CH3NH2	Hydrogen bonding, dipole-dipole, London dispersion

Physical Properties and Intermolecular Forces

• Surface Tension: Stronger intermolecular forces lead to higher surface tension.

• Boiling Point: Increases with stronger intermolecular forces.

• Vapor Pressure: Decreases with stronger intermolecular forces.

Example Table:

Physical Property	Compound: HOCH2CH2OH or CH3CH2CH2OH
Larger surface tension	HOCH2CH2OH (more hydrogen bonding)
Lower viscosity	CH3CH2CH2OH
Lower boiling point	CH3CH2CH2OH
Higher vapor pressure	CH3CH2CH2OH

Solution Concentration and Preparation

Concentration Units

• Molarity (M): Moles of solute per liter of solution.

• Molality (m): Moles of solute per kilogram of solvent.

• Parts per million (ppm): $ppm = \frac{\text{mg solute}}{\text{kg solution}}$

Example: Calculating the molarity of a solution given mass, volume, and density.

Solution Preparation

• To prepare a dilute solution from a concentrated stock, use:

$M_1V_1 = M_2V_2$

• Example: Preparing 1.00 L of 0.500 M HCl from concentrated HCl.

Energetics of Solution Formation

Enthalpy of Solution (ΔHsoln)

• ΔHsoln = ΔHsolute + ΔHsolvent + ΔHmix

• Can be exothermic or endothermic depending on the relative strengths of solute-solute, solvent-solvent, and solute-solvent interactions.

Example: Drawing and interpreting an enthalpy diagram for the dissolution of KBr.

Henry's Law

Henry's Law relates the solubility of a gas in a liquid to the partial pressure of the gas above the liquid:

$C = k_H P_{gas}$

• C = concentration of dissolved gas

• kH = Henry's law constant

• Pgas = partial pressure of the gas

Phase Diagrams

Phase diagrams show the state of a substance at various temperatures and pressures. Key features include:

• Triple Point: All three phases coexist.

• Critical Point: The endpoint of the liquid-gas boundary.

• Lines: Represent equilibrium between phases.

Hydration and Ion Properties

Enthalpy of Hydration

• Enthalpy of hydration increases with higher charge and smaller ionic radius.

• Order: Al3+ > Mg2+ > O2- > K+ > Ca2+

Solubility and Miscibility

• Polar substances are generally soluble in water; nonpolar substances are not.

• Hydrogen bonding increases solubility in water.

Example: Identifying which compounds are soluble in water and which can form hydrogen bonds.

Summary Table: Hydrogen Bonding Capability

Compound	Hydrogen Bonding? (Yes/No)
CH3CH2OH	Yes
CH3Cl	No
CH3NH2	Yes
CH4	No
CH3CN	No

Additional info:

• Some questions require drawing or interpreting diagrams (e.g., enthalpy diagrams, phase diagrams).

• Students are expected to show all work, including units, for full credit.

• Practice exam covers topics from Ch. 12 (Liquids, Solids & Intermolecular Forces) and Ch. 14 (Solutions), as well as related mathematical operations and lab techniques.